Magmatic signature of the closure of the northern branch of Neo-Tethys: Upper Paleocene-Middle Eocene magmatism at the boundary of Tavşanlı-Sakarya Zone (Turkey)

Abstract

Numerous plutons composed of granite, granodiorite, diorite-porphyry, monzonite, granodiorite-porphyry and diorite/microdiorite-porphyry occur at the boundary of the TavêanlÏ-Sakarya Zone, in the eastern part of the northwestern Anatolian magmatic belt, Turkey. These rocks belong to two different types: a medium-K calc-alkaline granodiorite series (with associated dykes and sub-volcanic rocks) and a shoshonitic series of granites. The rocks of the shoshonitic series have SiO2 from 67.5 to 75.6 wt.% with Mg# from 35.1 to 59.5, whereas the medium-K calc-alkaline series rocks have SiO2 between 54.6 and 67.7 wt.% with Mg# from 43.5 to 60.8. There is a clear enrichment of LILE with respect to the HFSE in all magmatic units of the region. These magmatic rocks reflect properties of collision-related arc magmatism in the various geochemical discrimination diagrams. The initial 87Sr/86Sr and 143Nd/144Nd istopic ratios of the magmatic units range from 0.705506 to 0.710902 and 0.512178 to 0.512594, respectively. Collision-related granitoids yielded a 40Ar/39Ar cooling age age of 59.13 ±1.87 Ma, and arc-related granitoids and associated sub-volcanic units 44.3 ±0.47 and 44.11 ±0.89 Ma. The data obtained revealed that continent-continent collision in the Paleocene together with the initiation of the closure of the Neo-Tethys took place between the Anatolide-Tauride Platform and Sakarya Plate from the end of the Cretaceous. The shoshonotic granite may cooled in the Middle Paleocene, as regards the subduction-accretion zone in which subduction impacts have been observed. The medium-K calc-alkaline magmatic products in the region were formed by partial melting of the continental lithospheric mantle caused by the upwelling of asthenospheric mantle after the subducted slab was delaminated